1. Field of the Invention
The present invention relates to a mobile station, and more particularly, to a mobile station apparatus for transmitting feedback information and method thereof.
2. Discussion of the Related Art
Generally, resource allocation is performed by a subchannel unit consisting of subcarriers in an orthogonal frequency division multiple access (hereinafter abbreviated OFDMA) system of a multicarrier type. In particular, multiple users share all subcarriers with each other by dividing the subcarriers. Through this, it is able to obtain a multi-user diversity gain on a frequency domain. In such an OFDMA based broadband mobile internet access system as WiBro (wireless broadband internet), every cell reuses the same frequency. And, it is able to maximize the throughput by applying adaptive modulation and coding (hereinafter abbreviated AMC) according to a corresponding received signal strength and inter-cell interference between adjacent cells.
In case of a system having a frequency reuse factor set to 1, the throughput is inevitably lowered due to the considerable interference between adjacent cells on a cell or sector boundary and a service outage situation is confronted. There is a method of enhancing performance on a cell boundary in using a frequency reuse factor set to 1. In particular, whole subcarrier is orthogonally divided into a plurality of frequency partitions. A plurality of the frequency partitions are appropriately arranged to enable each cell not to use some of the frequency partitions. Hence, the same channel interference between adjacent cells can be alleviated by not using some of the frequency partitions or performing transmission with low power. This scheme is called a fractional frequency reuse (hereinafter abbreviated FFR).
In order to apply the FFR to a real system, each mobile station estimates its precise location and then determines to use which band with reference to a frequency pattern provided to each cell. Yet, since a signal to interference ratio keeps changing continuously on the same band due to fading and mobile station's mobility in a real situation, the signal to interference ration should be dynamically considered to determine to use which frequency partition in the band allocated to each cell.
Thus, when the fractional frequency partition is allocated by cell unit, in order to use a resource dynamically according to the signal to interference ratio, inter-user fairness needs to be taken into consideration together with a given frequency reuse factor (hereinafter abbreviated FRF).
As mentioned in the foregoing description, when a plurality of frequency partitions are configured by orthogonally dividing while subcarrier in OFDMA system, it is able to consider diverse frequency reuse schemes to enable the frequency partition to be shared between cells. Concepts and properties of the frequency reuse schemes are described as follows.
First of all, if a frequency reuse factor gets closer to 1, a band available within a cell increases to raise band efficiency. Yet, inter-cell interference is increased by the same channel on a cell boundary or the like to raise an outage rate. On the contrary, the higher the frequency reuse factor increases, the less the interference due to the same channel between cells becomes. Yet, since an available band is reduced, band efficiency is lowered.
Regarding FFR, since an inter-cell interference level may not be relatively high for users located close to a base station in view point of whole cell, a service is provided using a frequency reuse factor set to 1 in a direction for maximizing whole cell capacity (i.e., using the whole subcarrier entirely). In case of using the frequency reuse factor set to 1, a service of good quality is provided to users on a cell boundary, in which the inter-cell interference is expected high, by reducing the inter-cell interference using a frequency reuse factor set to 3 (i.e., using a portion of segmentation 3 of each sector instead of using the whole subcarrier entirely).